There is a previous post dealng with your question...I am not sure now where it is but it is on the forum....somewhere. Use the search link above.

This plant ticks all the boxes for plants adapted to growing in degraded soils. It is
1.invasive
2. grows rapidly
3. unpalalatable to animals
4. it is trying to repair the degraded soil.

This is the repair mechanism Nature has given this plant....of course we all want to have perfect pastures with perfect soils and perfect fertility levels.

To prevent its spread follow the recommendations given by others elsewhere on this forum for increasing fertility levels and OM in your soil. Once this has been achieved the parramatta grass will be outcompeted by other plants.

Parramatta grass does do all the things above, but it will also grow in highly fertile soils and compete with kikuyu and other pastures (I have it growing on my place in Northern Rivers NSW). I would get rid of it if you can and let other weeds that are preferrably not grasses do the work. My favourites are thistles and fire weed.

It is amazing, as soon as the fertity builds up the grass out competes the thistles and fire weed. Just as Peter said it would.

Slashing will spread the parramatta grass seed around. Depending on how much you have try and cut the heads off and bag them. Then spray the plants. Once they are dead you can slash the weeds as normal. If your paddock is full of them, then just slash.

Peter would NOT advocate the use of toxic chemical sprays such as glyphosphates etc.,

But suggest you look at doing as "Foxdale' has done to control ST in another blog (look in Controlling weeds' blog) here or as Nik says just slash before the grass seeds.

Regardless, of the seed issue, once the fertility levels are restored the PG should not be an issue and if there are seeds of it in the ground it wont return unless the conditions are dire enough for it to be required.

I have been thinking a lot recently about the way we are taught to think about things.

As a practitioner of Chinese Medicine I was taught to think about things holistically we see a person as a collection of interacting systems not as a mechanical device.

However I find that in many other areas I still tend to think in a more Western linear mechanistic way and recognition of this has lead me to question the way weeds are looked at.

In western science almost everything is learned by separating and isolating things.
In theory we do this to provide proof by controlling the variables. In reality it is much more likely to be related to the way the brain functions.
Our brain has a very limited capacity to look at a sequence of facts, we rapidly become overwhelmed by raw and often conflicting data.
To deal with this overload, we make up narratives, stories we hold in our mind to explain and remember the data.
The moment we do this the data that does not fit into the narrative is dropped and soon forgotten.
Overtime the narrative becomes indispensable, it becomes excepted as what we know (to be true), at this point we tend to be unable to look at conflicting data. Our mind filters out that which does not fit our story.

This biological process occurs naturally and is unavoidable unless we set in place deliberate processes to loosen its grip on us.
Many years ago I was given the simplest of devices to loosen this grip, when I have used it it has never failed to be of benefit. The advice was to be a walking question mark.

So I now have some questions, as I understand it giant parramatta grass is a grass. What characteristics does it have that differ from other (preferred) grasses?

Duane mentioned that it is: unpalatable to animals and it is trying to repair the degraded soil.

I believe many grasses are stimulated to growth by grazing, if it is unpalatable this may not be the case as it would less frequently be grazed. It would probably crushed trampled and mulched by large herds of grazing animals.

With the idea that it is trying to repair the degraded soil, how? Does it have intelligence? Most plants can grow in fertile soils however the efficiency varies, does this grass have deeper roots to bring up nutrients?

If parramatta grass was cut and mulched and if the soil conditions were suitable would other pasture, that is stimulated by grazing, gain an advantage over the parramatta grass?

Lets assume for a moment that it is more efficient at selecting certain nutrients/minerals than preferred grasses, as it grows it concentrates these nutrients in the surface soil. If you kill it before it has concentrated these elements would you have improved the conditions for the preferred grasses? If seed is in the soil which plants will be more viable?

The problem as I see it with the standard story about weeds, is that they are invasive and hardy, that they push other plants out and must be destroyed. This is very much a mechanistic paradigm it pays no attention to the contrary data that we see all around us, that weeds are not capable of overtaking all the land, not to mention no thought given to what relationships it has to micro or macro flora and fauna. Nor to the energy, water and mineral cycles of the land.

Of course if we look at the holistic picture we may still decide the benefit of destroying the weed out ways the risks - we might

This is an old thread, but it comes up early in a Google search, so I thought I'd share that a friend of mine has set up a proper lab for propagating a fungus (Nigrospora oryzae) that helps crown rot form in Giant Parramatta Grass, and he's selling spores.